Abstract:

A method of making a disc for a computer disc drive and a disc made in
accordance with the same. The disc includes a deposited magnetic layer of
a thin film medium over a disc-shaped substrate. A master pattern having
a plurality of tracks is recorded on the disc. Each track on the disc
includes a plurality of magnetic islands, each having a size and magnetic
properties. The size and/or magnetic properties of one or more of the
magnetic islands of each track are modulated such that each track has a
modulation frequency, so as to imprint a magnetic topology on the disc.
The modulation frequency of each track is either a fundamental frequency
or an overtone of the fundamental frequency.

Claims:

1. A method of making a disc for a computer disc drive,
comprising:depositing a magnetic layer of a thin film medium over a
disc-shaped substrate;recording a master pattern on the disc, the master
pattern having a plurality of tracks, each track comprising a plurality
of magnetic islands, each magnetic island having a size and magnetic
properties;modulating at least one of the size and the magnetic
properties of the plurality of magnetic islands of each track such that
each track has a modulation frequency, so as to imprint a magnetic
topology on the disc,wherein the modulation frequency of each track is
one of a fundamental frequency or an overtone of the fundamental
frequency.

2. The method of claim 1, further comprising encoding a track ID in the
modulation of magnetic islands of at least one of the plurality of
tracks.

3. The method of claim 2, wherein the encoded track ID includes a phase
shift of the modulation frequency.

4. The method of claim 1, further comprising repeatedly writing a
predetermined subset of magnetic islands a predetermined number of times,
so as to increase the size of each of the predetermined subset of
magnetic islands.

5. The method of claim 4, wherein each repetition of writing the
predetermined subset of magnetic islands is shifted.

6. The method of claim 1, wherein the Hc of magnetic islands is modulated.

7. The method of claim 1, further comprising selectively applying a high
field and a reversed field so as to control a shape anisotropy of the
plurality of magnetic islands.

8. The method of claim 1 wherein the master pattern is recorded on the
disc using an electron beam.

9. The method of claim 1 wherein the master pattern is recorded on the
disc by applying an alternating high DC erase field and a reverse field.

10. A disc drive data storage system comprising:a data head adapted to
sense magnetic fields;a data storage disc having a plurality of magnetic
islands each having a magnetic field and a size and position such that
the data head senses the magnetic field for reading both magnetically
stored data and servo information, the servo information being encoded by
a specified position topology of magnetic islands and modulation of the
size of magnetic islands to align the data head with the data storage
disc.

11. The disc drive data storage system of claims 10, wherein the
modulation of the size of the magnetic islands encodes a track ID.

12. The disc drive data storage system of claims 11, wherein the encoded
track ID includes a phase shift of the modulation frequency.

13. The disc drive data storage system of claims 11, wherein the size of
each of a predetermined subset of magnetic islands is increased by
repeatedly writing the predetermined subset of magnetic islands a
predetermined number of times.

14. The disc drive data storage system of claims 13, wherein each
repetition of writing the predetermined subset of magnetic islands is
shifted.

15. The disc drive data storage system of claims 10, wherein the Hc of
magnetic islands is modulated.

16. The disc drive data storage system of claims 10, further comprising a
high field and a reversed field applied selectively so as to control a
shape anisotropy of the plurality of magnetic islands.

Description:

BACKGROUND OF THE INVENTION

[0001]The computer industry continually seeks to reduce size of computer
components and to increase the speed at which computer components
operate. To this end, it is desired to reduce the size required to
magnetically record bits of information. It is concomitantly important to
maintain the integrity of the information as size is decreased, and
magnetic storage of information must be virtually 100% error free.
Moreover, the methods used to reduce size, increase speed and maintain
information integrity in computer components must be very reproducible in
a manufacturing setting and must not be overly costly.

[0002]Disc drives which magnetically record, store and retrieve
information on disc-shaped media are widely used in the computer
industry. A write transducer is used to record information on the disc,
and a read transducer is used to retrieve information from the disc. The
reading and writing processes may be performed by a single structure,
i.e., a read-write transducer, or alternatively may be performed by
separate structures. In either case, the read transducer and the write
transducer are generally both located on a single magnetic head assembly.
The magnetic head assembly may include an air bearing slider which
suspends the magnetic head assembly relative to the rotating disc by
"flying" off air on the disc surface.

[0003]The magnetic head assembly is mounted on the end of a support or
actuator arm, which positions the head radially on the disc surface. If
the actuator arm is held stationary, the magnetic head assembly will pass
over a circular path on the disc known as a track, and information can be
read from or written to that track. Each concentric track has a unique
radius, and reading and writing information from or to a specific track
requires the magnetic head to be located above the track. By moving the
actuator arm, the magnetic head assembly is moved radially on the disc
surface between tracks.

[0004]The disc drive must be able to differentiate between tracks on the
disc and to center the magnetic head over any particular track. Most disc
drives use embedded "servo patterns" of magnetically recorded information
on the disc. Typical servo patterns are described in, for example, U.S.
Pat. No. 6,086,961, the disclosure of which is incorporated herein by
reference. The servo patterns are read by the magnetic head assembly to
inform the disc drive of track location. Tracks typically include both
data sectors and servo patterns. Each data sector contains a header
followed by a data section. The header may include synchronization
information to synchronize various timers in the disc drive to the speed
of disc rotation, while the data section is used for recording data.

[0005]Each servo pattern typically includes a "gray code" and a "servo
burst". The gray code indexes the radial position of the track such as
through a track number, and may also provide a circumferential index such
as a sector number. The servo burst is a centering pattern to precisely
position the head over the center of the track. Each servo burst includes
magnetic transitions on the inside of the track interleaved with magnetic
transitions on the outside of the track. If the magnetic head is centered
over the track, the signal read from the inside transitions will be equal
and opposite to the signal read from the outside transitions. If the
magnetic head is toward the inside of the track, the signal from the
inside transitions will predominate, and vice versa. By comparing
portions of the servo burst signal, the disc drive can iteratively adjust
the head location until a zeroed position error signal is returned from
the servo bursts indicating that the head is properly centered with
respect to the track.

[0006]Servo patterns are usually written on the disc during manufacture of
the disc drive, after the drive is assembled and operational. The servo
pattern information, and particularly the track spacing and centering
information, needs to be located very precisely on the disc. However, at
the time the servo patterns are written, there are no reference locations
on the disc surface which can be perceived by the disc drive.
Accordingly, a highly specialized device known as a "servo-writer" is
used during writing of the servo-patterns. Largely because of the
locational precision needed, servo-writers are fairly expensive, and
servo-writing is a time consuming process.

[0007]Most servo-writers operate using the disc drive's own magnetic head.
The servo-writer takes precise positional references to properly position
the heads in the disc drive for the writing of the servo patterns, and to
properly space the tracks with respect to one another on the disc
surface. For instance, the servo writer may have a physical position
sensor which takes a positional reference from the axis of the drive
spindle, and may have an optical position sensor which determines the
location of the magnetic heads with respect to the axis of the drive
spindle. With precise positioning of the magnetic head known, the
magnetic head of the disc drive is used to write the servo pattern on the
disc. The servo writer may also include a magnetic head which writes a
clock track at an outer radius of the disc. Once written, servo patterns
serve as the positional references on the disc surface used by the disc
drive during the entire life of the disc drive. The servo patterns are
used to properly center the head over the desired track prior to reading
or writing any data information from or to that track.

SUMMARY OF THE INVENTION

[0008]In accordance with one aspect of the present invention a method of
making a disc for a computer disc drive is provide. The disc is formed by
depositing a magnetic layer of a thin film medium over a disc-shaped
substrate and recording a master pattern on the disc. The master pattern
includes a plurality of tracks, each track having a plurality of magnetic
islands having a size and magnetic properties. At least one of the size
and the magnetic properties of the plurality of magnetic islands of each
track is modulated such that each track has a modulation frequency and
the modulation frequency is either a fundamental frequency or an overtone
of the fundamental frequency.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]The foregoing and other features of the present invention will be
more readily apparent from the following detailed description and
drawings of the illustrative embodiments of the invention wherein like
reference numbers refer to similar elements throughout the views and in
which:

[0010]FIG. 1 is a top plan view of a computer disc drive.

[0011]FIG. 2 is a side view of the computer disc drive of FIG. 1.

[0012]FIG. 3 is a greatly enlarged, cross-sectional perspective view of a
portion of the thin film magnetic disc of FIG. 1, schematically showing
magnetic flux.

[0013]FIG. 4 is a greatly enlarged top plan view of a servo pattern
portion of the thin film magnetic disc of FIG. 1, schematically showing
magnetic flux.

[0014]FIG. 4a is a greatly enlarged top plan view of an alternative servo
pattern portion of the thin film magnetic disc.

[0015]FIG. 5 illustrates a layout of the magnetic domains in accordance
with the present invention modulated to create a dot-topology, wherein
each track has a corresponding overtone frequency.

[0016]FIG. 6 illustrates a set of tracks in accordance with the present
invention having a fundamental dot frequency on top of which an overtone
having a lower frequency is generated.

[0017]FIG. 7 is a microscope image of a set of tracks made in accordance
with the present invention and a graph of the size and distribution of
the dot topology.

[0018]FIG. 8 illustrates a set of tracks made in accordance with the
present invention using a multi-pass on/off control is used to modulate
the dot size of specific dots.

[0019]FIG. 9 illustrates a process in accordance with the present
invention for controlling application of a magnetic field to control the
dot size in accordance with the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0020]The present invention relates generally to data storage devices, and
more particularly but not by limitation to disk media having patterned
magnetic islands pre-located on the disk for improved tracking.

[0021]FIGS. 1 and 2 represent a disc drive structure 10. Disc drive
assembly 10 includes disc pack 12 and E-block assembly 14. Disc pack 12
includes discs 16 stacked on drive spindle 18. During use of the disc
drive 10, drive spindle 18 rotates discs 16 about axis 20. Polar
coordinates 21 are established based on the geometry of disc 16, with the
perpendicular distance from axis 20 to any location on disc 16 being a
radius r, the circumferential dimension being Θ, and the axial
dimension being z.

[0022]E-block assembly 14 includes servo spindle 22 and a plurality of
actuator arms 24. Each actuator arm 24 carries one or two flexure arms or
suspension arms 26. Each suspension arm 26 supports an air bearing
magnetic head assembly 28 adjacent a surface of a disc 16. As disc 16
rotates about drive spindle 18 at a high speed (such as 10 m/s or higher)
relative to magnetic head assembly 28, the aerodynamic properties of
magnetic head assembly 28 cause assembly 28 to "fly" above the surface of
disc 16. The flying height of magnetic head assembly 28 above disc 16 is
a function of the speed of rotation of disc 16, the aerodynamic lift of
the slider of magnetic head assembly 28, and the spring tension in
suspension arm 26.

[0023]E-block assembly 14 is pivotable about pivot axis 30. As E-block
assembly 14 pivots, each magnetic head assembly 28 mounted at the tip of
its suspension arm 26 swings through arc 32. As each disc 16 rotates
beneath its respective magnetic head assembly 28, this pivoting motion
allows the magnetic head assembly 28 to change track positions on its
disc 16. Each disc 16 has a landing zone 34 where the magnetic head
assembly 28 lands, rests while the disc drive 10 is off, and takes off
from when the disc drive 10 is started up. Each disc 16 has a data zone
36 where the magnetic head assembly 28 flies over the disc 16 and
magnetically stores data.

[0024]To record information on the disc 16, the write transducer on
magnetic head assembly 28 creates a highly concentrated magnetic field.
During writing, the strength of the concentrated magnetic field directly
under the write transducer is greater than the coercivity of the
recording medium (known as "saturating" the medium), and grains of the
recording medium at that location are magnetized with a direction which
matches the direction of the applied magnetic field. The grains of the
recording medium retain their magnetization after the saturating magnetic
field is removed. As the disc 16 rotates, the direction of the writing
magnetic field is alternated based on bits of the information being
stored, thereby recording a magnetic pattern on the track directly under
the write transducer.

[0025]A magnetic medium 38 for disc 16 is illustrated in more detail in
FIG. 3. Magnetic medium 38 has a substrate 40 and an underlayer 42
deposited over the substrate 40. Substrate 40 is preferably a
nickel-phosphorous plated aluminum disc. Substrate 40 is relatively
thick, such as about 0.1 inches, and provides the structural integrity
for magnetic medium 38. Other materials, such as glass or
manganese-oxide, may also be suitable for substrate 40.

[0026]Underlayer 42 is formed of a non-magnetic material, such as chromium
or nickel-aluminum. Underlayer 44 is preferably 200 to 500 Angstroms
thick. Underlayer 42 sets up a seeding crystallographic structure for
proper crystal development in magnetic layer 44. Underlayer 42 may be
applied over substrate 40 by sputtering, and various sputter chamber
parameters may contribute to the effectiveness of underlayer 42. Other
materials such as Mo, W, Ti, NiP, CrV and Cr alloyed with other
substitutional elements have also been tried for underlayers, and workers
skilled in the art will appreciate that any one of these types of
underlayers may be found equivalently beneficial in applying the process
of the present invention.

[0027]Magnetic layer 44 of a magnetic material is applied over underlayer
42. Magnetic layer 44 is preferably formed of a cobalt-based alloy, such
as a cobalt-chromium-tantalum alloy. The preferred cobalt-based magnetic
layer 44 has a hexagonal close pack (HCP) crystal structure. Workers
skilled in the art will appreciate that other types of magnetic layers
may be equivalently used in practicing the present invention.

[0028]Magnetic layer 44 is preferably 100 to 300 Angstroms thick. Magnetic
layer 44 may be applied over underlayer 42 by sputtering, and various
sputter chamber parameters may contribute to the effectiveness of
magnetic layer 18.

[0029]To enhance the durability of the disc 16, overcoat 46 is deposited
over magnetic layer 44. Overcoat 46 helps reduce wear of magnetic media
36 due to contact with the magnetic read-write head assembly 28. Overcoat
46 also aids in corrosion resistance for the magnetic media 38. Overcoat
46 preferably is a layer of sputtered amorphous carbon. Other materials
which may be suitable for overcoat 46 include sputtered ceramic zirconium
oxide and amorphous films of silicon dioxide. Overcoat 46 can be about
100 to 150 Angstroms thick, with a preferred thickness of about 120
Angstroms. Any of the substrate 40, the underlayer 42 or the overcoat 46
may be textured as desired for beneficially affecting the tribology of
the particular disc drive system 10.

[0030]A lubricant layer 48 overlies overcoat 46. Lubricant layer 48 also
reduces wear and corrosion of the magnetic media 38. The lubricant 48 is
preferably a perfluoropolyether-based (PFPE) lubricant having a thickness
of 10 to 20 Angstroms. Overcoat 46 and lubricant 48, while not performing
a magnetic function, greatly affect the tribology and wear and corrosion
resistance in the disc drive system 10.

[0031]Magnetic layer 44, as originally deposited, is homogeneous in both
the radial and circumferential directions, and carries no magnetic
charge. After deposition of magnetic layer 44, information is
magnetically written on magnetic layer 44 as represented by + and -
magnetization signs 50, 52. In FIG. 3, multiple + and - magnetization
signs 50, 52 and multiple magnetic flux arrows 54 are shown to indicate
the direction of aligned magnetic domains and to indicate that numerous
aligned domains contribute to each magnetic transition. The writing of
the magnetic information occurs after disc 16 is fully fabricated
including deposition of overcoat 46 and lubricant 48. The magnetization
is believed to be made up of numerous aligned magnetic domains in the
structure of magnetic layer 44. Data is then read from magnetic medium 38
by sensing the alternating direction of magnetization, that is,
transition locations where the direction of aligned magnetic domains
reverses.

[0032]FIG. 4 schematically shows an areal portion of servo-pattern
information 56 magnetically recorded on disc 16. Magnetization signs 50,
52 indicate the direction of magnetization from the aligned magnetic
domains (i.e., "dots"). In FIG. 4, transition boundaries 57 between areas
of opposite magnetic domain alignment are shown in solid lines. The
boundaries 61 of each track 58 are shown in small dashed lines, and a
center line 59 of each track 58 is shown in larger dashed lines. The
boundaries 61 of each track 58 and the center lines 59 are not
recognizable by any physical properties of the magnetic medium 38, but
are shown for conceptual purposes only. During use of the disc drive 10,
the magnetic head assembly 28 is intended to be centered over a track 58
so the magnetic head assembly will accurately write information to and
read information from that track 58. In contrast to track boundaries 61
and center lines 59, each transition boundary 57 is magnetically sensed
by the magnetic head assembly 28 when it passes over the transition
boundary 57.

[0033]In the servo-patterns 56, substantially all of the magnetic domains
(i.e., dots) in magnetic medium 38 are aligned in one direction or the
other. While transition boundaries 57 are shown in FIG. 4 as sharply
defined areas, the true magnetic pattern may not have sharp transitions
between opposite directions of magnetization. The sharpness of the
transition boundaries on a recording medium is one of the basic
parameters in determining the density of the information which can be
stored on the recording medium.

[0034]Servo pattern information 56 is magnetically written on magnetic
medium 38 during manufacture of the disc drive 10. Each servo pattern
includes gray code information 60 and a servo burst 62. Gray code
information 60 contains indexing information to index each track 58 of
the disc 16. Each servo burst 62 includes a plurality of inside
transitions 64. Each servo burst 62 also includes a plurality of outside
transitions 66. Inside transitions 64 and outside transitions 66 are
precisely located on the disc 16 in the radial direction to define the
centerline 59 of each track 58, and to maintain very consistent spacing
between tracks 58.

[0035]During use of the disc drive 10, inside transitions 64 and outside
transitions 66 are used to center the magnetic head 28 over a track 58.
The signal read from servo bursts 62 depends on the radial position of
the magnetic head 28 with respect to the centerline 59 of a track 58. If
the magnetic head 28 is centered over the track 58, the signal read from
the inside transitions 64 will be equal to the signal read from the
outside transitions 66. If the magnetic head 28 is toward the inside of
the track 58, the signal from the inside transitions 64 will be stronger
than the signal from the outside transitions 66. If the magnetic head 28
is toward the outside of the track 58, the signal from the outside
transitions 66 will be stronger. By comparing portions of the servo burst
62 signal, the disc drive 10 can iteratively adjust the head 28 location
until a zeroed position error signal is returned from the servo bursts
62, indicating that the head 28 is properly centered with respect to the
track 58.

[0036]Traditionally, the servo patterns 56 are written on the magnetic
medium 38 during manufacture with a servo writer. Writing of the magnetic
signals requires two precisely positioned passes of the magnetic head 28
over each track 58: one for the inside transitions 64 and one for the
outside transitions 66. The magnetic head 28 typically writes a signal
which is around one track-width wide, considerably wider than either the
inside transitions 64 or the outside transitions 66. The only way the
servo bursts 62 can be written with such a head 28 is by erasing on each
pass part of what was written in the previous pass. The track-centered
gray code information 60 is written by matching the magnetization
direction during consecutive passes of the magnetic head 28. This process
of matching the magnetization of a previous pass to create a recorded
magnetic transition which is wider than the width of the recording head
is referred to as "stitching."

[0037]FIG. 4a shows an alternative configuration for servo bursts 62. This
configuration is quite similar to the configuration of FIG. 4, but the
inside transitions 64 are reversed with the outside transitions 66 in
every other track 58a, 58c, 58e. This servo burst configuration of FIG.
4a produces the strongest position error signal when the head is at a
track boundary 61. The position error signal decreases monotonically as
the head 28 approaches the center line 59, and becomes zeroed out when
the head 28 is centered over the center line 59. Writing of the magnetic
signals shown in FIG. 4a still requires two precisely positioned passes
of the magnetic head 28 over each track 58: one for the inside
transitions 64 and one for the outside transitions 66. The servo burst
configuration of FIG. 4a may be preferable to the servo burst
configuration of FIG. 4 due to the resultant position error signal.
Workers skilled in the art will appreciate that either configuration of
FIG. 4 or FIG. 4a may work suitably.

[0038]In accordance with one aspect of the present invention, the layout
of the magnetic domains, i.e., dot-topology, can be used to align the
head with the track and register its identification code. As illustrated
in FIG. 5, each dot can be modulated to create a pattern or dot-topology
500. The modulation can be encoded in the size, height (i.e., thick or
thin), or the magnetic properties (e.g., high or low) of the dot to
create the pattern. For example, topology-dots 510 are illustrated in
FIG. 5 as larger and darker than data-dots 520 and are thus easily
differentiated.

[0039]FIG. 5 illustrates four tracks: track 530, track 532, track 534, and
track 536. Each track has a corresponding overtone frequency which
registers the track. For example, if f0 is the dot frequency, track
536 has an overtone frequency of f0/2, track 534 has an overtone
frequency of f0/3, track 532 has an overtone frequency of f0/4,
and track 532 has an overtone frequency of f0/5. Further, it should
be noted that timing can be recovered from dot-topology.

[0040]The track-ID of each track can also be detected through the
dot-topology by detecting the phase shift of each track in the
dot-topology. FIG. 6 illustrates a set of tracks having a fundamental dot
frequency, f0, on top of which an overtone having a lower frequency
is generated. In FIG. 6, the overtone has a lower frequency of f0/9.
The modulated dots 620, illustrated as having a larger size and darker
color, have a relative phase shift from track to track, thus enabling the
detection of a relative track number. Proper initialization can be
accomplished using a servo/timing field, as known in the art, which sets
the clock for subsequent readings.

[0041]The dot-topology (i.e., servo) writing process preferably produces
tracks that form concentric circles about the center of rotation of the
disk spindle. The tracks would also be spaced at a desired track pitch
across the disk. Track pitch is defined as the distance between the
centerlines of the track, and in an ideal recording disk the track pitch
is equal between each individual track. Unfortunately, factors such as
mechanical vibrations that are asynchronous to disk rotation during the
servo writing process, along with disk defects and edge/transition noise
cause the tracks to form irregular concentric paths and generate
deviations in track pitch.

[0042]An electron beam recording can be used to modulate the dot size
during recording of the master pattern. In one embodiment, as illustrated
in FIG. 8, a multi-pass on/off control is used to modulate the dot size
of specific dots. FIG. 8 illustrates three tracks: track 810, track 820,
and track 830. By controlling whether the electron beam is on or off
during a pass of a spot, (e.g., FIG. 8 illustrates 15 passes), the size
of the dot can be modulated.

[0043]By way of example and with reference to track 810, both large dots
840 and small dots 850 can be created. Large dot 840 is comprised of
three overlapping dots which were created on successive passes of the
electron beam. Dot 842 was created on pass 0, dot 844 was created on pass
1, and dot 846 was created on pass 2. In contrast, small dot 850 is only
comprised of two dots--dot 852 and 854, which were created on pass 0 and
pass 1, respectively, of the electron beam. Large dot 840 and small dot
850 have difference Hc (Hk) and thus can be distinguished. The pattern of
large and small dots can be used to register and/or identify the track.

[0044]In a further alternative, the dot size can be controlled by
controlled application of a magnetic field, as illustrated by process 900
in FIG. 9. The first step 910 of the process 900 is to apply a high DC
erase field is applied, as in step 940 between dots (e.g., between dot
920 and 930). In the second step 950, a reverse field is applied 960,
thus creating the modulated spot 930. The reverse field preferably has a
field strength between that of the large and small dots. This technique
can be used to control the shape, size, and magnetic properties of each
dot.

[0045]It is to be understood that even though numerous characteristics and
advantages of various embodiments of the invention have been set forth in
the foregoing description, together with details of the structure and
function of various embodiments of the invention, this disclosure is
illustrative only, and changes may be made in detail, especially in
matters of structure and arrangement of parts within the principles of
the present invention to the full extent indicated by the broad general
meaning of the terms in which the appended claims are expressed. For
example, the particular elements may vary depending on the particular
application while maintaining substantially the same functionality
without departing from the scope and spirit of the present invention. In
addition, although the preferred embodiment described herein is directed
to a magnetic data storage device, it will be appreciated by those
skilled in the art that the teachings of the present invention can be
applied to optical devices without departing from the scope and spirit of
the present invention.